Y. Shopov (2012) Solar Impact on Global Climate Changes

8/9/2019 Y. Shopov (2012) Solar Impact on Global Climate Changes

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Solar impact on global climate changes

Y. Shopov

Citation: AIP Conference Proceedings 1551, 179 (2013); doi: 10.1063/1.4818867View online: http://dx.doi.org/10.1063/1.4818867

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Solar Impact on Global Climate Changes

Y. Shopov

University Center for Space Research and Technologies, St. Clement of Ohrid University at Sofia,

5 James Bourchier Blvd., BG-1164 Sofia, Bulgaria

e-mail: [email protected]

Abstract. Sunspots provide total solar irradiance (TSI) proxy records for the last 310 years. Speleothem achieves are stillonly of TSI proxy record providers, which allow extending of the TSI experimental records back to the pre- instrumental

times. Therefore they are very important for the assessment of the solar forcing of the climate in the pre-industrial era.

Using such speleothem records we demonstrated that variations of the solar irradiation which can produce climatic

variations are: (i) powerful prolonged solar cycles, which affect climatic variations and (ii) amplification of solarirradiance impact on climate by different potential non-linear mechanism or by a combination of them. Such

amplification is important at durations shorter than 11 years but can be more significant in timescales less than 1 year.

Keywords: global climate change, global warming, greenhouse gases, solar irradiance, solar cyclesPACS:92.60.Ry, 92.70.Aa, 92.70.-j, 92.70.Qr, 94.20.wq, 96.50.Wx, 96.60.Q, 96.60.qd, 96.60.-j, 96.60.Ub

1. INTRODUCTION

It was largely believed that global warming is caused by anthropogenic CO2 emissions, but recently the CoreWriting Team of 4-th IPCC [1] considers some natural processes, including solar ones, as a potential cause for part

of the global warming. However, recently another large group of distinguished scientists disputed man-made globalwarming claims [2]. The real situation might be somewhere in between. It reopens the debate on how much of the

global warming is produced by natural and how much by anthropogenic factors. In order to solve this task it isnecessary to assess precisely the potential natural causes of climatic changes. The most important such cause is solar

variability, which can affect the climate by various direct and indirect mechanisms.We live in greenhouse gases (GHG) but to estimate their influence over the climate system it is necessary to

know the natural climatic changes due to solar variations, because the Sun heats the Earth and therefore solarvariations provide the primary variations in the climate forcing. They produce a very strong climatic response. It is

useful to recognize the Sun as a variable, multiwavelength emitter which may be capable of significant modulationof terrestrial atmospheric dynamics (i.e., climate) through more than one of diverse physical coupling channels.

The fundamental source of all energy in the climate system is the Sun, and therefore variation in solar outputprovides a means for radiative forcing of climate change. Now its contribution to the global change receivesgrowing recognition. It is only since the late 1970s, however, and the advent of space-borne measurements of total

solar irradiance (TSI), that it has been clear that the solar constant does, in fact, vary with the solar rotation andthe 11- year solar cycle [3]. Before this discovery solar irradiance was considered to be constant, therefore Sun was

not considered as a potential source capable to change the climate. Tendency to such simplification at considering ofthe sources of climate changes decreases gradually, but still exist especially amongst ecologist community.

The C. George Marshall Institute report concludes that the most important natural climatic driver is the intensity

of solar radiation reaching the Earth, which is determined by changes in the Sun itself and that ...the Sun has beenthe controlling influence on climate in the last 100 years, with the greenhouse effect playing a smaller role [46].

Solar change might significantly alter climate. It might trigger several climate feedbacks and alter the GHG

(H2O, CO2, CH4, etc.) concentration [7]. Solar part of the forcing alone would account for 71% of the global mean

temperature variance, compared to 51% for the greenhouse gases part alone [8]. The sum of both forcing factors is122% thus suggesting that a part of the greenhouse gases emission is resulting from solar variations. Increased solar

irradiance warms Earth's oceans, which then triggers the emission of large amounts of carbon dioxide into theatmosphere (CO2 is less soluble in water at higher temperature). Therefore in Ref. [2] is stated that the common

Space Plasma Physics

AIP Conf. Proc. 1551, 179-188 (2013); doi: 10.1063/1.4818867 2013 AIP Publishing LLC 978-0-7354-1176-0/$30.00

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view that man's industrial activity is a deciding factor in global warming has emerged from a misinterpretation ofcause and effect relations.

Another possible coupling mechanism of increasing of the production of CO2by increasing of solar irradiance is

through dissolving of carbonate rocks by organic acids [9, 10] which has been heavily underestimated and might bethe major source of the variations of the atmospheric CO

2recorded in the polar ice cores as demonstrated by the

work of a large international program [11]. Production of the organic acids is determined by variations of the solarirradiance affecting photosynthesis and thermal decomposition of the soil, which is heated by solar radiation [10

13].In addition to the growing number of scientists expressing skepticism, an abundance of recent skeptical peer-

reviewed studies has cast considerable doubt about man-made global warming fears. Soon [14] found that Long-term climate change is driven by solar insolation changes, from both orbital variations and intrinsic solar magnetic

and luminosity variations... US Senate Report [2] states that the IPCC scenario underestimates the role of naturalvariability by proclaiming CO2to be the only reasonable source of additional energy in the planetary balance.

Long-term variations in the intensity of solar energy reaching the Earth are believed to cause climate change ongeological time-scales. New studies indicate that changes in the Suns magnetic field may be responsible for shorter-term changes in climate, including much of the climate of the 20th century. While the climate system is complex, it

is certain that any change in the amount of solar energy reaching the Earth will have an effect on climate [4].

FIGURE 1. Changes in the Suns magnetism represented by changes in the length of the Hale polarity or 22-year cycle

compared to the reconstructed northern hemispheres land temperature [15].

Changes in the Suns magnetism and in the reconstructed northern hemispheres land temperature are highly

correlated over the last 240 years (Fig. 1). The Suns magnetic changes are associated with changes in its totalenergy output, and may explain the close connection to terrestrial temperatures.

Earths surface temperature corresponds with the increase in solar radiation (Fig. 2).

FIGURE 2. Solar variability and surface temperature compared are the 11-year running mean of the sunspot number with globalaverage sea-surface temperature anomalies [16].


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A melting ice cap on Mars suggests that it is experiencing global warming, but without a greenhouse. Theseparallel global warmings observed simultaneously on Mars and on Earth are considered as a straight-line

consequence of the effect of the change in solar irradiance [2].

Board on Global Change, National Research Council [17] found that solar variations directly force the globalsurface temperature and modify the ozone and the structure of the middle atmosphere.

Short-time variations of the amount of interplanetary dust around the Sun are observed by Shopov et al. [18] atsolar eclipses.Shopov et al. [19] have also demonstrated that the amount of interplanetary dust between the Sun andthe Earth including that in the solar dust corona can vary fast enough to affect the recent climate change, but so farthere are no quantitative studies of this potential influence. There are no evidences that changes in the structure of

the solar corona can affect Earths climate [20].Variations of solar irradiance have been small during the period of direct satellite observations [21], but can be

much bigger during geological periods of time [10, 22, 23]. Air transparency can be modulated by cosmic rays [24]or by periodic variations of accretion of interplanetary dust produced by orbital inclination variations [25, 26].

Crowley [27] estimated that over the last 1000 yrs as much as 4164% of pre-anthropogenic decadal-scaletemperature variations have occurred due to changes in solar irradiance and volcanism. Volcanic eruptions stronglyaffect the transparency of the atmosphere for up to 23 years, but their appearance is non-periodic and cannot

be predicted. Therefore, they are not a subject of this study. Here we consider solar irradiance as potential driving

force of the Earths climate. For quantitative correlation, it is thus necessary to use experimentally determined recordsof solar insolation. Speleothem luminescence is still the only proxy producing such records for long spans of time. The

luminescence solar index represents solar radiation variations at the Earth's surface, so it is the most appropriatesolar proxy for study of the connection between Earth's climate and solar activity. In this study, we use such records

to study real variations of past insolation. The aim of this work is to study the influence of the variations of the TSI

on the climate change.

2. EXPERIMENTAL METHODS

The luminescence of calcite speleothems precipitated in vadose (air-filled) caves depends exponentially on soiltemperatures that are determined primarily by solar infrared radiation in the case when the cave is covered only

by grass or on air temperatures when there is forest or bush cover. In the first case, the microzonality of theluminescence detected in speleothems can be used as an indirect Solar Insolation index, and in the second as a

paleotemperature proxy. So, in terms of the dependence on cave site conditions we may speak about solar-sensitiveand temperature-sensitive paleoluminescence speleothem records as in tree ring records, but in our case records it

may depend entirely on temperature or on solar irradiation [28, 29].

The best samples for preparation of high-resolution paleoclimatic records are speleothems, which are secondarycave formations (stalagmites, stalactites, etc.) that may grow continuously for hundreds of thousands of years, preservingin their layers records of changes in different environmental parameters. Once formed, the majority remains

undisturbed and unchanged over geological time spans. Suitable speleothems are solid and with extremely puremineral composition (sometimes they are composed of just one single crystal). This allows reading of the records at

microscopic scales to achieve extremely high resolution, not yet obtainable from any other paleoclimatic terrestrialarchives. They are also datable by many independent absolute dating methods, unlike most other paleoclimatic archives.

This ensures the greater reliability and precision of the records obtained [30].Sampling is conducted along the growth axis of a speleothem. Laser luminescence microzonal analysis uses high optical

magnification, allowing a sampling resolution of less than a day in some instances [31]. Such resolution raises the questionis there such rapid real variation in the infiltrating solutions which precipitate the calcite? How great is the time lag in

speleothem records?

The time it takes for a molecule of water to pass through the system is its flow-through time, which can bemeasured by dye tracing. For example, Bottrell and Atkinson [32] placed fluorescent dyes at several sites at the base ofthe soil above a cave in the Pennine karst in England. The dyes traversed the 4590 m thick vadose zone and were

detected in the cave quite rapidly, sometimes within 24 h. Such rapid transport of fulvic and humic acids by the rainwaters could be responsible for the monthly variations observed in the speleothem luminescence of Cold Water Cave(Iowa) samples by Shopov et al. [31]. Longer-residence stored components of the flow will be responsible for longer-

term variations in the speleothem luminescence. At Cold Water Cave there is ~6 m of ancient till above thelimestone. This may delay some components of the speleothem drip water for several years, but others might pass

through via blocky fracturing in a few hours. The cave passage itself is quite quickly responsive to heavy rains(i.e., drips increase in amount within 24 h). A luminescence record from the same speleothem from Cold Water


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Cave, which is studied also in this paper, demonstrated high correlation (R2 = 0.90) with the Solar Irradianceindex obtained from direct observations since 1700 AD, with no detectable delay between the two records

[28]. This demonstrated that there was no delay longer than 3.8yrs (the time step of the correlated record) between

formation of the luminescent compounds and their incorporation into this particular stalagmite.

Van Beynen et al. [33] found very strong seasonal variations of concentration in the fulvic and humic acids

in dripping waters forming stalagmites in Marengo Cave, Indiana, allowing them to separate spring, summer,

fall and winter waters from each other. This suggests that there must be seasonal variations in luminescence of

these stalagmites which are produced by measured fulvic and humic acids. Van Beynen et al. [34] described dye trace

flow times of 4, 19 and 24 h from soils to sites of modern calcite deposition in this cave.

In this work, we use experimental luminescent speleothem proxy records of the insolation. Used instruments and

their characteristics are described in Shopov et al. [31].

3. RESULTS AND DISCUSSION

3.1. Past variations of the solar irradiance and their influence on climate

Sonett [35] found that a cycle with a period of about 900 yrs has intensity 57 times higher than that of the well-

known centennial cycle in the 14C solar proxy record. Stuiver and Braziunas [36] calculated MEM spectra of the same

record and claimed that Changes occur in the Sun's convective zone with a fundamental oscillatory mode of about 420 yrperiod and that centennial and sub-centennial cycles are about one-twentieth of the strength of this 420-yr cycle.Although the uncertainty of the proportion between intensities of different cycles in the spectra calculated by these

authors cannot be estimated, they suggest that longer solar cycles are stronger than the solar cycles detected by direct

measurements.The 11500-yr cycle was found previously to be the most intensive cycle in the

14C calibration record and was

interpreted to be of geomagnetic origin [37]. Our recent studies suggest that this is a solar cycle modulating thegeomagnetic field. Stoykova et al. [13] determined the solar origin of cycles with durations of 11 500, 4400, 3950,2770, 2500, 2090, 1960, 1670, 1460, 1280, 1195, 1145, 1034, 935, 835, 750 and 610 yrs. This was achieved by their

detection in proxy records of speleothem luminescence [10],14

C [37] and the intensity of the geomagnetic dipole

measured by [38]. The main variations in the last two records are known to be produced by the solar wind. The mostpowerful non-orbital cycle of 11 500 yrs is as powerful as the 23000-yr orbital cycle in the studied record, so this

solar luminosity cycle can produce climatic variations with intensity comparable to that of the orbital variations [23].

FIGURE 3.Real- Space Periodogramme of the luminescent insolation proxy record from Cold Water Cave, Iowa, US with

resolution of 3.78 px/yr.

Here we used Real-Space periodogramme analysis to compare the intensity of the cycles of speleothem

luminescence (representing cycles of solar radiation or air temperature) in a high-resolution record from ColdWater Cave, Iowa, USA. Obtained result (Figs. 3 and 4) demonstrates that the solar cycle of about 420 yrs has

intensity 3 times lower than this of the 2000-yr one. Known century solar cycle is even weaker than 420-yr one (Fig. 4).

Solar Cycles in CWC

0

0.01

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0.04

0.05

0 1000 2000 3000 4000

Cycle (Years)

lg(I)


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FIGURE 4.Short cycles presented in the Real-Space periodogramme of the luminescent insolation proxy record from Fig. 3.

We used Real-Space periodogramme analysis to calculate the intensity of cycles of speleothem luminescence

(representing temperature cycles) in a high-resolution composite record from Savi Cave (Fig. 5) near Trieste, Italy

[39], and a speleothem from Rats Nes t Cave, Alberta (Fig. 6) [40]. The power spectra on Fig. 5 demonstrate thatthe strongest cycles of soil temperature in the region are with durations of about 11, 22 and 70 years. Qian andZhu [41] found quasi-70-year climatic oscillations in the East Asia monsoon.

FIGURE 5.Intensity of cycles (in relative units) in a high-resolution composite luminescence soil or air temperature proxy

record. Original record SV1 from Savi Cave near Trieste, Italy used to calculate this periodogramme consists of 40106 data

points compiled of 16 overlapping scans covering the last 2028100 years. Its time step varies from 15.6 days to 19.9 days [39].

The Real-Space periodogrammes demonstrate that these speleothems recorded cycles of the soil temperaturewith durations of about 11 and 22 yrs (Figs. 5 and 6). The same cycles are detected also in speleothem proxy

records of paleo-air temperature. Paulsen et al. [42] used wavelet analysis to detect cycles of 33, 22, 11, 9.6 and 7.2

yrs in a 1270-yr high-resolution 18

O and 18

C record from China. The 11-yr solar cycle produces variations of thesolar constant with amplitude of less than 0.4% [21]. Cosmic rays influence on the atmospheric transparency

provides a mechanism of strong multiplication of solar variations on the solar radiation at the Earth's surface.Luminescence of speleothems from the Rats Nest Cave, Alberta, reproduces paleo-air temperatures [28], but

records from this cave exhibit a strong cycle of 425 yrs (Fig. 6), which is an important solar cycle [36]. This cycleprobably modulates air temperature in addition to the cosmic rays flux recorded by

14C variations. The same

records also contain centennial and bi-centennial solar cyclesWe studied a speleothem luminescence record from in Rats Nest Cave, Alberta, Canada [28, 40] and

demonstrated that this luminescence speleothem records is temperature-sensitive and represents a quantitative

proxy record of the air temperature at the cave site. They correlated this record with the meteorological record from

Solar Cycles in CWC

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0.01

0.02

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0.04

0.05

0 100 200 300 400 500 600 700 800 900 1000

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the near Banff station, Alberta, Canada and calibrated it in real temperature in degrees Celsius. Here we used Real-Space periodogramme analysis to compare the intensity of the cycles in this record. We obtained same cycles of the

past temperature (Fig. 6) as these in the luminescent insolation proxy record (Fig. 4). Not only duration of these

cycles is equal (in the frames of the experimental error), but even their relative intensities are quite similar in bothsolar and temperature proxy record. This fact suggests that considered solar cycles with duration from a century to

450 years might strongly affect Earths climate not only on global scales but even in local locations.

FIGURE 6.Cycles of paleotemperature in Rats Nest Cave, Alberta, Canada, in relative units.

Presence of 22 and 11 year solar cycles in the paleotemperature record from Rats Nest Cave, Alberta, Canadasuggests that variation of the solar constant with amplitude of less than 0.4% can produce measurable variation of

the air temperature. It might be result of the cosmic ray or other amplification mechanism.In fact the 11-year solar sunspot cycle consists of a bunch of discrete sub-cycleswith duration from 7 to 17 years

from solar cycle maximum to the next maximum. To illustrate this property of the 11-year solar sunspot cycle wecalculated a Real-Space periodogramme of the entire annual Wolf numbers record for the last 310 years using the

same code as the one used to calculate periodogrammes on Figs. 36. So obtained results are fully comparable and

demonstrate similar structures of the obtained 11-year solar cycle in all periodogrammes of the luminescent proxy

records (Figs. 36) and Wolf numbers (Fig. 7).

FIGURE 7. Intensity of cycles of the annual Wolf numbers. This periodogramme demonstrates strong splitting of the 11-year

cycle into discrete sub-cycles.

0

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Lg(I)[R.U.]

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3.2. Potential amplification mechanisms of multiplication of solar irradiance impact on

climate

Atmospheric circulation dramatically masks solar impact on climate, especially at short time scales. It is one of

the main reasons for the popular belief that there is no solar impact on climate. Recent studies suggest that suchimpact exists [43] and it is far stronger than expected from the small variations of the solar irradiance, but it is better

visible in long time series of sea surface temperature (Fig. 2) and global land temperature (Fig. 1).Stott et al. [44] states that current climate models underestimate the observed climate response to solar forcing

over the twentieth century as a whole, indicating that the climate system has a greater sensitivity to solar forcingthan do models. Taking into account that the amplitude of the total variation of the solar constant over the twentiethcentury was only 3.9 Wm2(0.28% of the solar constant) [45] and even only 1.6 Wm2accordingly [46] it is evident

that there are one or more mechanisms of non-linear amplification of the solar impact on the climate. Suchmechanism is still not established.

About 54% of the decadal- and longer-scale variations of the 11-year running mean record of the annual-mean,

worldwide-averaged land temperature taken from NASA GISS database over the last 100 years can be optimallyattributed to intrinsic total solar irradiance change, and 38% to effects of increased anthropogenic greenhouse gases

(GHGs), leaving a small 8% unexplained variation [8, 47]. But the inferred solar radiative forcing change (slightlyless than 1 W m

20.5% of the total solar irradiance [48, 49], converted into forcing at the top of atmosphere) issignificantly smaller than the estimated global forcing of 2.4 +/ 0.4 W m2 resulting from the increases of the

anthropogenic GHG concentrations over the last 100 years [50]. There is thus an inconsistency between weak solar

radiative forcing and large climatic response. However, there are several ways in which this discrepancy might beresolved.

First, it might be argued that the solar radiative forcing of about 1 Wm2

and the response of 0.27 C (54% of thetotal observed warming of about 0.5 C) are consistent with the IPCC range of climate sensitivity. However, a

different sensitivity would be necessary to reconcile the anthropogenic greenhouse forcing of 2.4 W m2

with theresponse of 0.19 C (38% of 0.5 C), so the seeming contradiction reappears.

A second way to resolve this contradiction would be to invoke other, as yet undetermined, radiative forcingnegatively correlated with GHG forcing. One example is an incomplete accounting of aerosols in the radiative

budget of the climate system.A third type of resolution is possible if the Sun-climate connection were viewed through the perspective of

climate dynamics, in which the simple thermodynamics of direct radiative heating of the terrestrial atmosphere and

surface is not the sole mechanism capable of yielding significant responses.So this third type of resolution may be subdivided into (a) purely internal natural variability; and (b) mechanisms

involving the external triggering of internally-determined climate shifts, or external forcing amplified by internalfeedback mechanisms.

Subtype (a) would invoke the possibility of purely internal natural climatic variability that might correlate by

coincidence with solar variability. Alternatively, a robust mechanism that can serve to trigger or amplify (or both,i.e., resolution subtype (3b) the response to changes in the external solar radiative or corpuscular (or both) forcing

would also resolve this inconsistency between weak solar forcing and large climate response. Tinsley [51] and Soon

et al. [52] suggest additional, possible modulation mechanisms related to effects of solar and cosmic-ray chargedparticles.

There are several examples of feedback mechanisms in subtype (b) of the third category of resolutions of the

discrepancy. Promising coupling mechanisms include solar UV forcing change [53, 54] and stratospheric ozone

change (see, e.g., Refs. [55, 56]), both of which have been shown to be capable of amplifying solar irradianceforcing by modulation of both the amount and distribution of upward-propagating planetary waves which then cause

significant changes to the circulation patterns of the low and middle atmospheres [57].A link between cosmic rays intensity and cloud cover has been discovered by Ohring and Clapp [58] and proven

by comprehensive measurements [24]. Cosmic rays may serve as nucleation centers for condensation of the water in

the clouds [24]. The galactic cosmic rays flux at the Earth is strongly modulated by the solar wind [59]. Stronger

solar wind produces a lower cosmic rays flux and may result in less cloud cover. Solar luminosity variations corre-late with the solar wind strength. The weaker cloud cover produces higher sky transparency and higher solar

insolation at the Earth's surface, and vice versa. The cosmic rays-cloud cover mechanism may thus multiply theimpacts of solar irradiance variation on the insolation at the Earth's surface. Therefore, this effect should

produce a strong positive correlation between the solar activity (especially solar irradiance variations) and globaltemperatures. In many cases this is observed despite the very small variations of solar irradiance [60].


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Svensmark and Friis-Christensen [24] measured variations in the cloud cover of 3% during an average 11-yrsolar cycle and estimated that this caused variation of the insolation of 0.81.7 W m

2. Such variation is able to

produce significant climatic variation.

The integrated sky transparency may vary with up to 25% between clearest and cloudiest days [61], but ifintegrated over 1 yr this variation is less than 0.65% from year to year if a normal distribution of sunny days is

assumed. In fact, even lower variations should be expected. This suggests that cosmic rays modulation of the climatecan be more significant during short per iods, especially those produced by the solar rotation [62, 63].

However, none of these mechanisms has been generally accepted as adequate to resolve the Sun-climateinconsistency, because of a lack of either theoretical proof of robustness or empirical studies resolving the effects of

individual mechanisms. At this time, it remains possible that climatic change caused by solar variability ismodulated mainly by only one of these mechanisms, by a combination of more than one of them, or by mechanisms

still not identified.

4. CONCLUSION

Variations of the solar irradiation can produce climatic variations owing to:

1. Powerful prolonged solar cycles, which affect the climatic variations;

2. Amplification of solar irradiance impact on climate by cosmic rays changing the transparency of the air, by

another mechanism or by a combination of more than one mechanism. Such amplification is important at durations

shorter than 11 years but can be more significant in timescales less than 1 year.

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the 5th International Conference on Climate Change: The Karst Record (KR5)(Chongqing, China, June 25, 2008), p. 66.

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